Semiconductor memory device and manufacturing method thereof

ABSTRACT

The present invention relates to a semiconductor memory device having a SRAM in which a memory cell comprises a pair of transmission transistors and a flip-flop circuit containing a pair of driver transistors and a pair of load transistors, wherein: a first conductive film interconnection formed from a first conductive film which is set on a semiconductor substrate, constitutes respective gate electrodes of said driver transistors, load transistors and transmission transistors; an inlaid interconnection set in a first insulating film lying on said semiconductor substrate, constitutes one of a pair of local interconnections cross-coupling a pair of input/output terminals in said flip-flop circuit; and a second conductive film interconnection formed from a second conductive film which is set on a second insulating film lying on said first insulating film, constitutes the other one of said pair of local interconnections. The present invention can provide a SRAM whose memory cell size is readily reduced without unduly increasing the number of the steps in the manufacturing method thereof. Further, the present invention can improve the α-ray soft error resistance of the SRAM.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Divisional Application of application Ser. No.10/046,792, filed on Jan. 15, 2002 and issued as U.S. Pat. No.6,900,513.

TECHNICAL FIELD

The present invention relates to a semiconductor memory device and amanufacturing method thereof and more particularly to a semiconductormemory device having a SRAM (Static Random Access Memory) and amanufacturing method thereof.

BACKGROUND OF THE INVENTION

With reference to a drawing, the basic structure of a SRAM memory cellthat is a semiconductor memory element is described below.

As shown in a circuit diagram of FIG. 22, a SRAM memory cell is composedof a flip-flop circuit that functions as an information storage sectionand a pair of transmission transistors T₁ and T₂ that control theconduction between data lines (bit lines, BL₁ and BL₂) which serve forwriting and reading of the information and the flip-flop circuit. Theflip-flop circuit is made of, for example, a pair of CMOS (ComplementaryMetal Oxide Semiconductor) inverters and each CMOS inverter contains adriver transistor D₁ (D₂) and a load transistor P₁ (P₂).

One side of source/drain regions in each transmission transistor T₁ (T₂)is connected to drains of a load transistor P₁ (P₂) as well as a drivertransistor D₁ (D₂), and the other side thereof is connected to a bitline BL₁ (BL₂). Further, gates of a pair of the transmission transistorsT₁ and T₂ each form a part of a word line WL and are connected with eachother.

The gates of the driver transistor D₁ and the load transistor P₁ whichconstitute one of the CMOS inverters are connected to the drains (thestorage node N₂) of a driver transistor D₂ and a load transistor P₂which constitute the other of the CMOS inverters. Further, the gates ofthe driver transistor D₂ and the load transistor P₂ which constitute thelatter of the CMOS inverters are connected to the drains (the storagenode N₁) of the driver transistor D₁ and the load transistor P₁ whichconstitute the former of the CMOS inverters. In effect, a pair of CMOSinverters are arranged such that the input/output section of each CMOSinverters may be cross-coupled with the gate of the other CMOS inverterthrough one of a pair of interconnections L₁ and L₂, which are calledthe local interconnections.

Further, a reference voltage (V_(SS), for example, GND) is applied tothe source region of each one of the driver transistors D₁ and D₂, and asupply voltage (V_(CC)) is applied to the source region of each one ofthe load transistors P₁ and P₂.

The SRAM cell described above has excellent element characteristics suchas the high noise tolerance and the small stand-by power. Further, forthe SRAM cell of this sort, in view of element characteristics,selection of the materials and layout are carefully made so as not tolose symmetry of the element structure (in other words, to preventimbalance from occurring) within the limits of possibility.

However, the SRAM cell described above has a problem that a cell areatends to become considerably large, due to requirements to have 6transistors in one memory cell and isolate p-type MOSs from n-type MOSswithin one and the same cell as well as the need of numerousinterconnections. Another disadvantage it has is the large number of thesteps in the manufacturing method thereof.

Therefore, with respect of the structure of the 6-transistors type SRAMcell and manufacturing method thereof, various propositions have beenmade so far.

For example, in Symp. on VLSI Tech., p. 64 (1998) by M. Inohara et al.,a method of forming each one of a pair of local interconnections throughthe metal damascene process is disclosed. In this method, two tungsten(W) local interconnections which are damascene interconnections areformed in different layers, respectively, and thereby formation of across-couple is achieved. It is, therein, described that, because atungsten plug reaching an active region on a substrate and one (a lowerlayer) of the local interconnections are formed by making their openingssimultaneously, this SRAM memory cell can be fabricated without settingadditional photomasks or increasing the number of the steps infabrication. Nevertheless, in this method, because the other one (anupper layer) of the local interconnections should be formed in such away that its disposition could avoid any contact with the lower layer ofthe local interconnections, a reduction in cell size attained cannot besufficiently large.

Further, in Japanese Patent Application Laid-open No. 251457/1999, it isdescribed that, in fabrication of a 6-transistors type cell, a pair oflocal interconnections are both formed with a metal damascene process,and besides disposed on one and the same layer. Yet, in this method,too, it is difficult to achieve a sufficient reduction in cell size,since a pair of local interconnections must be disposed so as not tocome into contact with each other.

Meanwhile, in Japanese Patent Application Laid-open No. 260510/1997,with the object of reducing in size of the memory cell and improving theα-ray soft error resistance, there is disclosed an element structuredescribed below. A similar structure is also described by F. Ootsuka etal. in IEDM, p. 205 (1998).

In this structure, a pair of local interconnections to form a crosscouple are formed by applying etching to different conductive layers,respectively. An upper layer of local interconnections is disposed so asto overlap a lower layer of local interconnections, and these localinterconnections separated by an insulating film (a capacity insulatingfilm) constitute a capacitor element.

However, for such an element structure, a contact hole must be formedseparately for each one of a pair of local interconnections so that asubstantially large number of steps are required in its fabrication.Further, in this structure, the local interconnections are laid in arelatively wide range, extending even as far as the top of a gateelectrode, with a thin insulating film lying therebetween. When aconductive film pattern is to be formed on such an uneven substratesurface, there arises a problem that superfluous parts of the conductivefilm may remain at unrequired positions because, in performingpatterning of the conductive film by means of anisotropic etching, it isdifficult to remove portions of the conductive film around steppedparts. Further, when a capacitor insulating film is to be formed on suchan uneven surface, the film thickness thereof tends to increase aroundthe stepped parts. On the other hand, if the film thickness around thestepped parts is to be made satisfactorily thin, there may arise anotherproblem that the film thickness in the flat region becomes excessivelythin, which may result in damage to insulation thereof. In short,formation of a thin and, at the same time, even capacitor insulatingfilm is difficult to achieve.

In view of the above discussion, it would be desirable to provide atechnology capable to reduce easily the memory cell size of the SRAMwithout unduly increasing the number of the steps in the manufacturingmethod thereof. It would also be desirable to provide a technology toimprove the α-ray soft error resistance of the SRAM.

SUMMARY OF THE INVENTION

The present invention can provide a SRAM whose memory cell size isreadily reduced without unduly increasing the number of the steps in themanufacturing method thereof. Further, the present invention can improvethe α-ray soft error resistance of the SRAM.

The present invention relates to a semiconductor memory device having aSRAM in which a memory cell comprises a pair of transmission transistorsand a flip-flop circuit containing a pair of driver transistors and apair of load transistors, wherein:

a first interconnection formed from a first electrical conductor whichis set on a semiconductor substrate, constitute respective gateelectrodes of said driver transistors, load transistors and transmissiontransistors;

a second interconnection including a second electrical conductor whichis formed within a trench that is set in a first insulating film lyingon said semiconductor substrate, constitutes one of a pair of localinterconnections cross-coupling a pair of input/output terminals in saidflip-flop circuit;

a third interconnection which is formed on a second insulating filmlying on a region including the top surface of said secondinterconnection, constitutes the other one of said pair of localinterconnections; and

either said second interconnection or said third interconnection has aburied conductive section which is formed to fill up the inside of saidtrench.

Further, the present invention relates to the semiconductor memorydevice as set forth above, wherein:

said second interconnection and said third interconnection have anoverlapping section separated by said second insulating film, and

said second interconnection and said third interconnection, togetherwith said second insulating film lying therebetween, constitute acapacitor element.

Further, the present invention relates to the semiconductor memorydevice as set forth above, wherein:

said second electrical conductor is disposed so as to come in contactwith

-   -   a drain region constituting a first driver transistor which is        one of said pair of driver transistors;    -   a drain region constituting a first load transistor which is one        of said pair of load transistors and has a gate electrode formed        from a first interconnection A, the gate electrode being in        common to said first driver transistor, and    -   a first interconnection B which constitutes a gate electrode of        a second driver transistor which is the other one of the pair of        driver transistors as well as a gate electrode of a second load        transistor which is the other one of the pair of load        transistors; and

said third interconnection is in contact with

-   -   a contact section connected to said first interconnection A;    -   a contact section connected to a drain region of said second        driver transistor; and    -   a contact section connected to a drain region of said load        transistor.

Further, the present invention relates to a semiconductor memory devicehaving a SRAM in which a memory cell comprises a pair of transmissiontransistors and a flip-flop circuit containing a pair of drivertransistors and a pair of load transistors, wherein:

a first conductive film interconnection formed from a first conductivefilm which is set on a semiconductor substrate, constitutes respectivegate electrodes of said driver transistors, load transistors andtransmission transistors;

an inlaid interconnection set in a first insulating film lying on saidsemiconductor substrate, constitutes one of a pair of localinterconnections cross-coupling a pair of input/output terminals in saidflip-flop circuit; and

a second conductive film interconnection formed from a second conductivefilm which is set on a second insulating film lying on said firstinsulating film, constitutes the other one of said pair of localinterconnections.

Further, the present invention relates to the semiconductor memorydevice as set forth above, wherein

said second conductive film interconnection is disposed so as to overlapat least a portion of a top surface of said inlaid interconnection, withsaid second insulating film lying therebetween; and

said inlaid interconnection and said second conductive filminterconnection, together with said second insulating film lyingtherebetween, constitute a capacitor element.

Further, the present invention relates to the semiconductor memorydevice as set forth above; wherein

said second conductive film interconnection is disposed so as to coverat least a portion of a lateral face of said inlaid interconnection,with said second insulating film placed therebetween; and

said inlaid interconnection and said second conductive filminterconnection, together with said second insulating film lyingtherebetween, constitute a capacitor element.

Further, the present invention relates to the semiconductor memorydevice as set for the above, wherein:

said inlaid interconnection is disposed so as to come in contact with

-   -   a drain region constituting a first driver transistor which is        one of said pair of driver transistors;    -   a drain region constituting a first load transistor which is one        of said pair of load transistors and has a gate electrode formed        from a first conductive film interconnection A, the gate        electrode being in common to said first driver transistor; and    -   a first conductive film interconnection B which constitutes a        gate electrode of a second driver transistor which is the other        one of the pair of driver transistors as well as a gate        electrode of a second load transistor which is the other one of        the pair of load transistors; and

said second conductive film interconnection is in contact with

-   -   a contact section to reach said first conductive film        interconnection A;    -   a contact section to reach a drain region of said second driver        transistor; and    -   a contact section to reach a drain region of said second load        transistor.

Further, the present invention relates to the semiconductor memorydevice as set forth above, wherein said first conductive filminterconnection B branches off between the drain region of said seconddriver transistor and the drain region of said second load transistor,and this branched section of interconnection comes into contact withsaid inlaid interconnection.

Further, the present invention relates to the semiconductor memorydevice as set forth above, wherein a contact region between saidbranched section of interconnection and said inlaid interconnectioncontains a point that is, seen from the substrate top surface,equidistant from any among a group of said contact section to reach thefirst conductive film interconnection A, said contact section to reachthe drain region of the second driver transistor and said contactsection to reach the drain region of the second load transistor.

Further, the present invention relates to a semiconductor memory devicehaving a SRAM in which a memory cell comprises a pair of transmissiontransistors and a flip-flop circuit containing a pair of drivertransistors and a pair of load transistors, wherein:

a first conductive film interconnection formed from a first conductivefilm which is set on a semiconductor substrate, constitutes respectivegate electrodes of said driver transistors, load transistors andtransmission transistors;

an inlaid interconnection which is set in a first insulating film lyingon said semiconductor substrate and a stacked electrode which is set onsaid inlaid interconnection constitutes one of a pair of localinterconnections cross-coupling a pair of input/output terminals in saidflip-flop circuit;

a second conductive film interconnection formed from a second conductivefilm which is formed on a second insulating film lying on said firstinsulating film, constitutes the other one of said pair of localinterconnections; and

said second conductive film interconnection is disposed so as tooverlap, at least, a portion of a top surface and a portion of a lateralface of said stacked electrode with said second insulating film placedtherebetween, and said stacked electrode and said second conductive filminterconnection, together with said second insulating film lyingtherebetween, constitute a capacitor element.

Further, the present invention relates to a semiconductor memory devicehaving a SRAM in which a memory cell comprises a pair of transmissiontransistors and a flip-flop circuit containing a pair of drivertransistors and a pair of load transistors, wherein:

a first conductive film interconnection formed from a first conductivefilm which is set on a semiconductor substrate, constitutes respectivegate electrodes of said driver transistors, load transistors andtransmission transistors;

an inlaid interconnection set in a first insulating film lying on saidsemiconductor substrate, constitutes one of a pair of localinterconnections cross-coupling a pair of input/output terminals in saidflip-flop circuit;

within a trench that is formed in a third insulating film lying on saidfirst insulating film, there is provided with an in-trench electrodefilm, which comes in contact with said inlaid interconnection at thebottom of the trench;

a second conductive film which is set on a second insulating film lyingon said third insulating film, and a buried electrode which is formed byfilling up said trench, with said in-trench electrode film as well assaid second insulating film being placed therebetween, constitute theother one of said pair of local interconnections; and

said buried electrode and said in-trench electrode film, together withsaid second insulating film lying therebetween, constitute a capacitorelement.

Further, the present invention relates to a semiconductor memory devicehaving a SRAM in which a memory cell comprises a pair of transmissiontransistors and a flip-flop circuit containing a pair of drivertransistors and a pair of load transistors, wherein:

a first conductive film interconnection formed from a first conductivefilm which is set on a semiconductor substrate, constitutes respectivegate electrodes of said driver transistors, load transistors andtransmission transistors;

within a trench that is formed in a first insulating film lying on saidsemiconductor substrate, there is provided with an in-trench conductivefilm, which constitutes one of a pair of local interconnectionscross-coupling a pair of input/output terminals in said flip-flopcircuit;

a second conductive film which is set on a second insulating film lyingon said first insulating film, and a buried electrode which is formed byfilling up said trench, with said in-trench electrode film as well assaid second insulating film being placed therebetween, constitute theother one of said pair of local interconnections; and

said buried electrode and said in-trench electrode film, together withsaid second insulating film lying therebetween, constitute a capacitorelement.

Further, the present invention relates to the semiconductor memorydevice as set forth above, wherein a refractory metal silicide layer isformed on the surface of every gate electrodes, source regions and drainregions of said pair of driver transistors, said pair of loadtransistors and said pair of transmission transistors.

Further, the present invention relates to a method of manufacturing asemiconductor memory device having a SRAM in which a memory cellcomprises a pair of transmission transistors and a flip-flop circuitcontaining a pair of driver transistors and a pair of load transistors,which comprises the steps of:

forming, on a semiconductor substrate, active regions to form respectivesource regions and drain regions of said driver transistors, said loadtransistors and said transmission transistors;

forming, on said semiconductor substrate, a first conductive film; andthereafter patterning this first conductive film to form a firstconductive film interconnection that is to serve as an interconnectionto constitutes respective gate electrodes of said driver transistors,said load transistors and said transmission transistors;

forming, on said semiconductor substrate, a first insulating film; andthereafter forming, in this first insulating film, an inlaidinterconnection as one of a pair of local interconnectionscross-coupling a pair of input/output terminals in said flip-flopcircuit; and

forming, on said first insulating film, a second insulating film, andthereafter forming a second conductive film and, then, patterning thissecond conductive film to form a second conductive film interconnectionas the other one of said pair of local interconnections.

Further, the present invention relates to the method of manufacturing asemiconductor memory device as set forth above; wherein

said second conductive film interconnection is disposed so as to overlapat least a portion of a top surface of said inlaid interconnection, withsaid second insulating film lying therebetween; and

said inlaid interconnection and said second conductive filminterconnection, together with said second insulating film lyingtherebetween, constitute a capacitor element.

Further, the present invention relates to a method of manufacturing asemiconductor memory device having a SRAM in which a memory cellcomprises a pair of transmission transistors and a flip-flop circuitcontaining a pair of driver transistors and a pair of load transistors,which comprises the steps of:

forming, on a semiconductor substrate, active regions to form respectivesource regions and drain regions of said driver transistors, said loadtransistors and said transmission transistors;

forming, on said semiconductor substrate, a first conductive film; andthereafter patterning this first conductive film to form a firstconductive film interconnection that is to serve as an interconnectionto constitute respective gate electrodes of said driver transistors,said load transistors and said transmission transistors;

forming, on said semiconductor substrate, a first insulating film, andthereafter forming, in this first insulating film, an inlaidinterconnection as one of a pair of local interconnectionscross-coupling a pair of input/output terminals in said flip-flopcircuit;

exposing a part of a lateral face of said inlaid interconnection; and

forming a second insulating film on said first insulating film and theexposed section of said inlaid interconnection; and thereafter forming asecond conductive film and, then, patterning this second conductive filmso as to overlap the top surface and a portion of the lateral face ofsaid inlaid interconnection, with said second insulating film placedtherebetween; and thereby forming a second conductive filminterconnection which constitutes the other one of said pair of localinterconnections, which provides a capacitor element composed of saidsecond conductive film interconnection and the top surface and a portionof the lateral face of said inlaid interconnection, together with saidsecond insulating film lying therebetween.

Further, the present invention relates to the method of manufacturing asemiconductor memory device as set forth above, wherein:

said inlaid interconnection is formed so as to come in contact with

-   -   a drain region constituting a first driver transistor which is        one of said pair of driver transistors;    -   a drain region constituting a first load transistor which is one        of said pair of load transistors and has a gate electrode formed        from a first conductive film interconnection A, the gate        electrode being in common to said first driver transistor, and    -   a first conductive film interconnection B which constitutes a        gate electrode of a second driver transistor which is the other        one of the pair of driver transistors as well as a gate        electrode of a second load transistor which is the other one of        the pair of load transistors; and

said second conductive film interconnection is formed to come intocontact with every one of contact sections which are made by forming,concurrently, a contact hole to reach said first conductive filminterconnection A, a contact hole to reach the drain region of saidsecond driver transistor, and a contact hole to reach the drain regionof said second load transistor; and thereafter filling up these contactholes with a conductive material.

Further, the present invention relates to the method of manufacturing asemiconductor memory device as set forth above, wherein said firstconductive film interconnection B is formed into the branched shape inwhich branching off takes place between the drain region of said seconddriver transistor and the drain region of said second load transistor,and said inlaid interconnection is formed so as to come into contactwith this branched section of interconnection.

Further, the present invention relates to the method of manufacturing asemiconductor memory device as set forth above, which further comprisesthe step of forming a refractory metal silicide layer on the surface ofevery source regions and drain regions of said pair of drivertransistors, said pair of load transistors and said pair of transmissiontransistors as well as on the surface of said first conductive filminterconnection which constitutes gate electrodes thereof.

In the present invention, by forming a pair of local interconnectionsfrom different conductive layers, it becomes possible to dispose thesetwo local interconnections partially overlapped with each other so thatthe occupied area of the memory cell can be well reduced.

Further, in the present invention, because a pair of the localinterconnections separated by an insulating film can constitute acapacitor element, α-ray soft error resistance can be prevented fromlowering, which may take place along with miniaturization of the memorycell size or a decrease in operation voltage.

Further, in the present invention, when one of the localinterconnections set in a lower layer is made of an inlaidinterconnection, formation of this lower layer local interconnection canbe made, together with formation of a contact plug so that fabricationthereof can be achieved with the small number of steps. Further, whenone of the local interconnection set in a lower layer is made of aninlaid interconnection, due to improved planarity, it becomes possible,with ease, to form thinly as well as uniformly a capacitor insulatingfilm and the other one of local interconnections which are set in anupper layer, which may improve the yield and element characteristics.

Further, in the present invention, through formation of a refractorymetal silicide layer that is a low-resistance material on source/drainregions or gate electrodes, a still higher speed operation can beattained without relying upon a symmetry of the SRAM structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of a SRAM memory cell in a semiconductormemory device according to the present invention.

FIG. 2 is a plan view in explaining an embodiment of a SRAM memory cellin a semiconductor memory device according to the present invention.

FIG. 3 is a cross-sectional view in explaining an embodiment of a SRAMmemory cell in a semiconductor memory device according to the presentinvention.

FIG. 4 is a plan view in explaining a manufacturing method of a SRAMmemory cell in a semiconductor memory device according to the presentinvention.

FIG. 5 is a cross-sectional view in explaining a manufacturing method ofa SRAM memory cell in a semiconductor memory device according to thepresent invention.

FIG. 6 is a cross-sectional view in explaining a manufacturing method ofa SRAM memory cell in a semiconductor memory device according to thepresent invention.

FIG. 7 is a plan view in explaining a manufacturing method of a SRAMmemory cell in a semiconductor memory device according to the presentinvention.

FIG. 8 is a cross-sectional view in explaining a manufacturing method ofa SRAM memory cell in a semiconductor memory device according to thepresent invention.

FIG. 9 is a plan view in explaining a manufacturing method of a SRAMmemory cell in a semiconductor memory device according to the presentinvention.

FIG. 10 is a cross-sectional view in explaining a manufacturing methodof a SRAM memory cell in a semiconductor memory device according to thepresent invention.

FIG. 11 is a plan view in explaining a manufacturing method of a SRAMmemory cell in a semiconductor memory device according to the presentinvention.

FIG. 12 is a cross-sectional view in explaining a manufacturing methodof a SRAM memory cell in a semiconductor memory device according to thepresent invention.

FIG. 13 is a plan view in explaining a manufacturing method of a SRAMmemory cell in a semiconductor memory device according to the presentinvention.

FIG. 14 is a cross-sectional view in explaining a manufacturing methodof a SRAM memory cell in a semiconductor memory device according to thepresent invention.

FIG. 15 is a plan view in explaining a manufacturing method of a SRAMmemory cell in a semiconductor memory device according to the presentinvention.

FIG. 16 is a cross-sectional view in explaining a manufacturing methodof a SRAM memory cell in a semiconductor memory device according to thepresent invention.

FIG. 17 is a plan view in explaining a manufacturing method of a SRAMmemory cell in a semiconductor memory device according to the presentinvention.

FIG. 18 is a cross-sectional view in explaining a manufacturing methodof a SRAM memory cell in a semiconductor memory device according to thepresent invention.

FIG. 19 is a plan view in explaining a manufacturing method of a SRAMmemory cell in a semiconductor memory device according to the presentinvention.

FIG. 20 is a cross-sectional view in explaining a manufacturing methodof a SRAM memory cell in a semiconductor memory device according to thepresent invention.

FIG. 21 is a cross-sectional view in explaining another embodiment of aSRAM memory cell in a semiconductor memory device according to thepresent invention.

FIG. 22 is a circuit diagram of a conventional SRAM memory cell.

FIG. 23 is a cross-sectional view in explaining another embodiment of aSRAM memory cell in a semiconductor memory device according to thepresent invention.

FIG. 24 is a cross-sectional view in explaining a manufacturing methodof a SRAM memory cell in a semiconductor memory device according to thepresent invention.

FIG. 25 is a cross-sectional view in explaining a manufacturing methodof a SRAM memory cell in a semiconductor memory device according to thepresent invention.

FIG. 26 is a cross-sectional view in explaining a manufacturing methodof a SRAM memory cell in a semiconductor memory device according to thepresent invention.

FIG. 27 is a cross-sectional view in explaining another embodiment of aSRAM memory cell in a semiconductor memory device according to thepresent invention.

FIG. 28 is a cross-sectional view in explaining a manufacturing methodof a SRAM memory cell in a semiconductor memory device according to thepresent invention.

FIG. 29 is a cross-sectional view in explaining a manufacturing methodof a SRAM memory cell in a semiconductor memory device according to thepresent invention.

FIG. 30 is a cross-sectional view in explaining a manufacturing methodof a SRAM memory cell in a semiconductor memory device according to thepresent invention.

FIG. 31 is a cross-sectional view in explaining a manufacturing methodof a SRAM memory cell in a semiconductor memory device according to thepresent invention.

FIG. 32 is a cross-sectional view in explaining a manufacturing methodof a SRAM memory cell in a semiconductor memory device according to thepresent invention.

FIG. 33 is a cross-sectional view in explaining another embodiment of aSRAM memory cell in a semiconductor memory device according to thepresent invention.

FIG. 34 is a cross-sectional view in explaining a manufacturing methodof a SRAM memory cell in a semiconductor memory device according to thepresent invention.

FIG. 35 is a cross-sectional view in explaining a manufacturing methodof a SRAM memory cell in a semiconductor memory device according to thepresent invention.

FIG. 36 is a cross-sectional view in explaining a manufacturing methodof a SRAM memory cell in a semiconductor memory device according to thepresent invention.

FIG. 37 is a cross-sectional view in explaining a manufacturing methodof a SRAM memory cell in a semiconductor memory device according to thepresent invention.

FIG. 38 is a cross-sectional view in explaining a manufacturing methodof a SRAM memory cell in a semiconductor memory device according to thepresent invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Preferred embodiments of the present invention are described below.

As shown in FIG. 1, a memory cell in a SRAM of the present invention,composed of a pair of driver transistors D₁ and D₂, a pair of loadtransistors P₁ and P₂, and a pair of transmission transistors T₁ and T₂,is disposed in an intersection region of a word line WL and a pair ofbit lines BL₁ and BL₂. A pair of driver transistors D₁ and D₂ as well asa pair of transmission transistors T₁ and T₂ consist of n-channel typeones, while a pair of load transistors P₁ and P₂ consist of p-channeltype ones.

A pair of driver transistors D₁ and D₂ and a pair of load transistors P₁and P₂ make up a flip-flop circuit that functions as an informationstorage section for memorizing 1 bit information. This flip-flop circuitis composed of a pair of CMOS inverters, and each CMOS inverter containsa driver transistor D₁ (D₂) and a load transistor P₁ (P₂).

One side of source/drain regions in each transmission transistor T₁ (T₂)is connected to drains of the load transistor P₁ (P₂) as well as thedriver transistor D₁ (D₂), and the other side thereof is connected to abit line BL₁ (BL₂). Further, gates of a pair of transmission transistorsT₁ and T₂ each form a part of a word line WL and are connected with eachother.

The gates of the driver transistor D₁ and the load transistor P₁ whichconstitute one of the CMOS inverters are connected to the drains (thestorage node N₂) of the driver transistor D₂ and the load transistor P₂which constitute the other of the CMOS inverters. Further, the gates ofthe driver transistor D₂ and the load transistor P₂ which constitute thelatter of the CMOS inverters are connected to the drains (the storagenode N₁) of the driver transistor D₁ and the load transistor P₁ whichconstitute the former of the CMOS inverters. In effect, a pair of CMOSinverters are arranged such that the input/output section of each CMOSinverters may be cross-coupled with the gate of the other CMOS inverterthrough one of a pair of interconnections L₁ and L₂, which are calledthe local interconnections.

Further, a reference voltage (V_(SS), for example, GND) is applied tothe source region of each one of the driver transistors D₁ and D₂, and asupply voltage (V_(CC)) is allied to the source region of each one ofthe load transistors P₁ and P₂.

First and Second Embodiments

Next, First and Second Embodiments of the present invention aredescribed below.

In the First Embodiment, a pair of local interconnections L₁ and L₂ aredisposed in two different layers, with the local interconnection in alower layer being formed of an inlaid (damascene) interconnection andthe local interconnection in an upper layer, formed of a conductive filmin the form of a plate. Further, the disposition of these localinterconnection is arranged in such a way that, seen from the topsurface (the top surface plane) of the substrate, a portion of the upperlayer local interconnection (the plate-shaped interconnection) overlapsat least a portion of the top surface of the lower layer localinterconnection (the inlaid interconnection), with an insulating filmlying therebetween. Herein, the lower layer local interconnection (theinlaid interconnection) and the upper layer local interconnection (theplate-shaped interconnection), separated by an insulating film,constitute a capacitor element.

Since the inlaid interconnection has a considerable thickness (a lengthin the direction of the depth) and the plate-shaped interconnection of aconductive film has a large top surface area, both interconnections canachieve a good reduction in interconnection resistance, compared withinterconnections made of a conductive thin film in the form of a minuteline.

Referring to the drawings, the structure of the above SRAM memory cellis described specifically in detail below.

FIG. 2 is a plan view of a memory cell, and FIGS. 3( a) and (b) arecross-sectional views taken along the line a–a′ and the line b–b′ ofFIG. 2, respectively. Any insulating film, bit line, and plug to connectto the bit line are, herein, omitted from the plan view.

6 transistors comprised in the memory cell are formed in active regionsARs each surrounded by element isolation regions 5 on a semiconductorsubstrate made of a single crystal silicon. N-channel type drivertransistors D₁ and D₂ as well as transmission transistors T₁ and T₂ areformed in a p-type well region, while p-channel type load transistors P₁and P₂, in an n-type well region.

A pair of transmission transistors T₁ and T₂ are each composed of n-typesource/drain regions 13 a formed in the active region of p-type well, agate oxide film 7 formed on the surface of this active region, and agate electrode 8 formed on this gate oxide film 7. This gate electrode 8has, for example, a layered structure made of a doped polycrystallinesilicone film and a refractory metal silicide film (a tungsten silicidefilm, a cobalt silicide film, a titanium silicide film or the like), andis formed with a word line WL as one body. The word line WL is setrunning in a first direction (the left-right direction in FIG. 2) and,along this first direction, a pair of transmission transistors aredisposed, adjacent to each other. Further, the deposition of the pair oftransmission transistors is arranged in such a way that the direction ofthe gate length thereof coincides with a second direction (thetop-bottom direction in FIG. 2), perpendicular to the first direction.

A pair of driver transistors D₁ and D₂ are each composed of n-typesource/drain regions 13 a formed in the active region of p-type well, agate oxide film 7 formed on the surface of this active region, and agate electrode 9 or 10 formed on this gate oxide film 7. This gateelectrode 9 or 10 has, for example, a layered structure made of a dopedpolycrystalline silicone film and a refractory metal silicide film (atungsten silicide film, a cobalt silicide film, a titanium silicide filmor the like). The drain region of the driver transistor D₁ is formed inthe active region in common with one of the source/drain regions of thetransmission transistor T₁, while the drain region of the drivertransistor D₂ is formed in the active region in common with one of thesource/drain regions of the transmission transistor T₂.

A pair of load transistors P₁ and P₂ are each composed of p-typesource/drain regions 13 b formed in the active region of n-type well, agate oxide film 7 formed on the surface of this active region, and agate electrode 9 or 10 formed on this gate oxide film 7. The gateelectrode 9 of the load transistor P₁ is formed with the gate electrodeof the driver transistor D₁ as one body, while the gate electrode 10 ofthe load transistor P₂ is formed with the gate electrode of the drivertransistor D₂ as one body.

The driver transistor D₁ is disposed between the transmission transistorT₁ and the load transistor P₁ in the afore-mentioned second direction.The driver transistor D₂ is disposed between the transmission transistorT₂ and the load transistor P₂ in the afore-mentioned second direction.The disposition of a pair of driver transistors and a pair of loadtransistors are arranged in such a way that the direction of any gatelength thereof coincides with the afore-mentioned first direction.

It is preferable to set a refractory metal silicide layer (not shown inthe drawings) such as s titanium silicide layer or a cobalt silicidelayer on the surface of every source/drain regions of a pair of drivertransistors, a pair of load transistors and a pair of transmissiontransistors, for the purpose of reducing the sheet resistance and thecontact resistance caused by the contact plug.

On the lateral face of every gate electrode that is contained in a pairof driver transistors, a pair of load transistors and a pair oftransmission transistors, there is formed a sidewall 12. Further, on thetop of the gate electrode, there may be set a cap layer (not shown inthe drawings) made of a silicon oxide film or the like.

On the top of any one of six transistors, a silicon nitride film 14 isformed, and, on the top of this silicon nitride film 14, a firstinterlayer insulating film 15 is formed to a thickness of 300–1000 nm orso from PSG (Phospho-Silicate Glass), BPSG (Boron Phosphorous SilicateGlass) or such.

Within this first interlayer insulating film 15, there is formed aninlaid interconnection 16 (L₁) that is one of a pair of localinterconnections. To form this inlaid interconnection 16 (L₁), a trenchis formed in the first interlayer insulating film 15 and filled up witha conductive metal such as tungsten. While one end section of thisinlaid interconnection 16 (L_(l)) is electrically connected to the drainregion of the driver transistor D₁, the other end section thereof iselectrically connected to the drain region of the load transistor P₁.Further, the central section of the inlaid interconnection 16 (L₁) iselectrically connected to the gate electrode 10, which serves for bothof the driver transistor D₂ and the load transistor P₂. This gateelectrode 10 branches off between the drain region of the drivertransistor D₂ and the drain region of the load transistor P₂ towards thedirection of transistors D₁ and P₁, and this branched section comes intocontact with the central section of the inlaid interconnection 16. Thiscontact section is preferably disposed at a position, seen from the top,substantially equidistant from any of three contact plugs 18, 19 and 20described below. In this instance, although the inlaid interconnectioncan be zonal and besides, seen from the top, rectangular in shape, itmay take the shape of a zone deflected in the central section, beingdrawn aside towards the side of transistors D₂ and P₂, with respect toboth end sections, as shown in the plan view of FIG. 2. In this way, anample margin can be attained.

On the first interlayer insulating film 15 in which the inlaidinterconnection 16 (L₁) is formed, a second interlayer insulating film17 is formed to a thickness of 10–150 nm or so from a silicon oxide filmor the like. Further, contact holes formed through this secondinterlayer insulating film 17 and the first interlayer insulating film15 are filled with a conductive metal such as tungsten to set contactplugs. These contact plugs are plugs 19–26 being in contact withrespective source/drain regions of 6 transistors and a plug 18 being incontact with the gate electrode 9, which is used by the drivertransistor D₁ and the load transistor P₁ in common.

On the top of the second interlayer insulating film 17, there is formeda local interconnection 27 (L₂) from TiN or such to a thickness of100–200 nm or so. The local interconnection 27 (L₂) is set connectingelectrically to the plug 18 that is connected with the gate electrode 9,common to the driver transistor D₁ and the load transistor P₁, the plug19 that is connected with the drain region of the driver transistor D₂,and the plug 20 that is connected with the drain region of the loadtransistor P₂. Further, the disposition of the local interconnection 27(L₁) is arranged in such a way that a portion thereof overlaps, atleast, a portion of the top surface of the afore-mentioned inlaidinterconnection 16 (L₁) which is the other local interconnection, withthe second interlayer insulating film 17 lying therebetween. The localinterconnection 27 (L₂) and the inlaid interconnection 16 (L₁),separated by the second interlayer insulating film, constitute acapacitor element. In view of the effect of a capacitor element, thelocal interconnection 27 (L₂) is preferably set covering the top surfaceof the inlaid interconnection 16 (L₁) as much as possible, and, in thestructure shown in FIG. 2, the local interconnection 27 (L₂) covers theentire top surface of the inlaid interconnection 16 (L₁).

Further, in order to facilitate the connection with the via plugs whichare further connected to the above layers, on the contact plugs 21–26,there are provided with respective rectangular conductive film patterns28–33, which are concurrently formed with the local interconnection 27(L₂) by patterning.

On the top of the second interlayer insulating film 17 in which thelocal interconnection 27 (L₂) is formed, a third interlayer insulatingfilm 34 is formed from a silicon oxide film or the like and, thereon, asupply voltage line 41 to apply a supply voltage V_(CC), a referencevoltage line 42 to apply a reference voltage V_(SS), are formed alongthe afore-mentioned first direction. The supply voltage line 41 iselectrically connected through via plugs 36 and 37 set in the thirdinterlayer insulating film 34 and contact plugs 22 and 23 set in thefirst and second interlayer insulating films, to the source regions ofthe load transistors P₁ and P₂, respectively. The reference voltage line42 is electrically connected through via plugs 35 and 38 set in thethird interlayer insulating film 34 and contact plugs 21 and 24 set inthe first and second interlayer insulating films, to the source regionsof the driver transistors D₁ and D₂, respectively. Theseinterconnections can be formed, for example, from a patterned aluminiumfilm or a layered film comprising an aluminium film and films of TiN orthe like which may be laid over the aluminium film as an anti-reflectioncoating film, and laid below the aluminium film as a barrier metal film.

Further, in order to facilitate the connection with the via plugs whichare further connected to the above layers, on the top of the plugs 39and 40 which are set in the third interlayer insulating film 34 formaking electrical connection to one side of the source/drain regions ofthe transmission transistors T₁ and T₂, there are provided withrespective rectangular conductive film patterns 43 and 44, which areconcurrently formed with the supply voltage line 41 and the referencevoltage line 42 by patterning.

On the top of the third interlayer insulating film 34 in which thesupply voltage line 41 and the reference voltage line 42 are formed, afourth interlayer insulating film (not shown in the drawings) is formedfrom a silicon oxide film or the like and, thereon, a pair of bit linesBL₁ and BL₂ (not shown in the drawings) are formed along theafore-mentioned second direction. One of the bit lines BL₁ iselectrically connected, through a via plug set in the fourth interlayerinsulating film, and the via plug 40 set in the third interlayerinsulating film and the contact plug 26 set in the first and secondinterlayer insulating films, to one side of the source/drain regions ofthe transmission transistor T₁. The other bit line BL₂ is electricallyconnected, through a via plug set in the fourth interlayer insulatingfilm, and the via plug 39 set in the third interlayer insulating filmand the contact plug 25 set in the first and second interlayerinsulating films, to one side of the source/drain regions of thetransmission transistor T₂. These interconnections can be formed, forexample, from a patterned aluminium film or a layered film comprising analuminium film and films of TiN or the like which may be laid over thealuminium film as an anti-reflection coating film, and laid below thealuminium film as a barrier metal film.

As the second embodiment of the present invention, a SRAM memory cellmay have a structure that is the same as the above structure but thearrangement of a capacitor element, wherein deposition of localinterconnections is arranged in such a way that, seen from the topsurface of the substrate, a portion of the upper layer localinterconnection (the plate-shaped interconnection) overlaps, at least, aportion of the top surface of the lower layer local interconnection (theinlaid interconnection) with an insulating film lying therebetween, andbesides a portion of the upper layer local interconnection (theplate-shaped interconnection) partially covers the lateral face (a faceparallel to the direction of the depth) of the lower layer localinterconnection (the inlaid interconnection) with an insulating filmlying therebetween. In this structure, a capacitor element is formed notonly on the top surface of the lower layer local interconnection (theinlaid interconnection) but also on the lateral face thereof so that thecapacitance of the element can be raised significantly. Across-sectional view (corresponding to the plan view of FIG. 2) of oneexample of this embodiment is shown in FIG. 21.

Next, taking a manufacturing method of the first embodiment as anexample, a method of manufacturing a SRAM memory cell in a semiconductormemory device of the present invention is described, with reference tothe drawings. The plan view, herein, are presented with some insulatingfilms appropriately omitted therefrom.

First, on the principal plane of a semiconductor substrate 1 made of ap-type single crystal silicon, a silicon oxide film 2 and a siliconnitride film 3 are formed, in succession, by a known method. Using, as amask, a photoresist in the shape of a prescribed pattern which is formedby a known method, dry etching is then applied thereto and the siliconnitride film 3 and the silicon oxide film 2 are patterned. After that,using the remained silicon nitride film 3 and silicon oxide film 2 as amask, the semiconductor substrate 1 is dry etched to form trenches 4 forelement isolation (FIG. 4 and FIG. 5). In the drawings, hereat, regionsindicated by AR are active regions and, in this step, trenches forelement isolation are formed in regions other than ARs. Further, aregion indicated by MR, which is encircled by a dotted line represents aregion for one memory cell. A plurality of memory cells are disposed insuch a way that, with each side of a rectangle indicated by MR that runsalong the afore-mentioned first direction (the left-right direction inFIG. 4) being used as a line of symmetry, the shapes indicated by ARbetween neighbouring memory cells in the afore-mentioned seconddirection (the top-down direction in FIG. 4) become line symmetricimages (mirror operation), while, with each side of a rectangleindicated by MR that runs along the afore-mentioned second directionbeing used as a datum line, the shapes indicated by AR betweenneighbouring memory cells in the afore-mentioned first direction becomeimages shifted to the first direction (parallel translation). It is alsopossible to dispose memory cells so that the shapes indicated by ARbetween every two neighbouring memory cells may become line symmetric,with respect to the common side of rectangles indicated by MR.

Next, as shown in FIG. 6, the inside of the trenches 4 is filled with asilicon oxide film, and element isolation regions 5 are formed. Theformation of the element isolation regions 5 can be made as follows. Ona semiconductor substrate 1 in which trenches 4 are set, a silicon oxidefilm is formed thick enough to fill up the inside of the trenches 4completely by the CVD (Chemical Vapour Deposition) method, andthereafter, using the silicon nitride film 3 as a stopper, etch back orchemical mechanical polishing (CMP) is applied to the thickly formedsilicon oxide film to remove the silicon oxide film other than portionsthereof lying inside of the trenches 4, whereby the element isolationregions 5 are formed.

Next, after the silicon nitride film 3 and the silicon oxide film 2 onthe semiconductor substrate 1 are removed by etching, a thin siliconoxide film (a sacrifice oxide film) 2 a with a thickness of 10–30 nm orso is formed and then a resist 6 is formed in a region where loadtransistors P₁ and P₂ are to be formed, as shown in FIG. 7 and FIG. 8.Using this resist 6 and the afore-mentioned oxide film 2 a as a mask anda through film, respectively, ion-implantation of p-type dopants (forexample, boron) is applied thereto to form a p-type well region whereload transistors D₁ and D₂ and transmission transistors T₁ and T₂ are tobe formed later. Next, after removing the resist 6, another resist isformed on the p-type well region, and using this resist and theafore-mentioned oxide film 2 a as a mask and a through film,respectively, ion implantation of n-type dopants (for example,phosphorus or arsenic) is applied thereto to form an n-type well regionwhere load transistors P₁ and P₂ are to be formed later.

Next, after removing the silicon oxide film (the sacrifice oxide film) 2a lying on the semiconductor substrate, a gate oxide film is formed bythe thermal oxidation method, and then a doped polycrystalline siliconefilm is formed. Thereat, a refractory metal silicide film such as atungsten silicide film may be formed on the doped polycrystallinesilicone film, and then a silicone oxide film for formation of a caplayer may be formed thereon. Next, using a photoresist formed into aprescribed pattern as a mask, dry etching is performed and thereby thedoped polycrystalline silicone film and the gate oxide film (togetherwith the refractory metal silicide film and the silicon oxide film, inthe case that this silicide film and oxide film are formed thereon) areconcurrently patterned, and a gate electrode 8 (a word line WL) of thetransmission transistors T₁ and T₂, gate electrodes 9 and 10 of thedriver transistors D₁ and D₂ and load transistors P₁ and P₂ are formed,as shown in FIG. 9 and FIG. 10.

Next, a transistor structure shown in FIG. 11 and FIG. 12 is formed asfollows. Using a resist formed on the n-type well region as a mask, ionimplantation of n-type dopants (for example, phosphorus or arsenic) isapplied thereto with a relatively small dose to form LDD (Lightly-DopedDrain) regions 11 in the p-type well region. After removing this resist,using another resist formed on the p-type well region as a mask, ionimplantation of p-type dopants (for example, boron) is similarly appliedthereto to form LDD regions 11 in the n-type well region. Next, afterthis resist is removed, a silicon oxide film is formed on the substrateby the CVD method, and by subjecting this silicon oxide film to etchback, sidewalls 12 are formed on the lateral faces of the gateelectrodes. The sidewalls may be formed from a layered film made offilms of oxide-nitride-oxide or films of nitride-polysilicon. Afterthat, using a resist formed on the n-type well region as a mask, ionimplantation of n-type dopants is applied thereto with a relativelylarge dose to form n-type source/drain regions 13 a in the p-type wellregion. Subsequently, after removing this resist, using another resistformed on the p-type well region as a mask, ion implantation of p-typedopants is similarly applied thereto to form p-type source/drain regions13 b in the n-type well region.

After this step is completed, on the source/drain regions, refractorymetal silicide films are preferably formed. First, on the semiconductorsubstrate, a refractory metal (for example, Ti or Co) film is formed bythe sputtering method or such. Next, by annealing, the refractory metalfilm and the source/drain regions are made to react with each other, andthereafter unreacted refractory metal is removed by etching, whereby arefractory metal silicide film is formed on the source/drain regions.If, in the step described above, no tungsten silicide film or siliconoxide film is formed on the gate electrodes, refractory metal silicidefilms are, hereat, formed on the gate electrodes.

Next, after a silicon nitride film 14 is formed on the semiconductorsubstrate by the CVD method, an interlayer insulating film 15 is formedfrom PSG, BPSG or the like. Using a photoresist formed into a prescribedpattern as a mask, dry etching is then performed to make openingsthrough the first interlayer insulating film 15 as well as the siliconnitride film 14, and thereby trenches to reach the substrate surface andthe gate electrodes are formed. By filling up these trenches with aconductive metal such as W, a local interconnection 16 (L₁) made of aninlaid interconnection is formed, as shown in FIG. 13 and FIG. 14.Thereat, filling up the trenches with a conductive metal is carried outas follows. A barrier metal film is formed on the substrate includingthe inside of the trenches, for example, from a layered film of Ti/TiNor the like by the sputtering method or such, and thereafter, by the CVDmethod or such, a conductive metal film is formed from tungsten or thelike so as to fill up the trenches, and, subsequently, CMP is applied tothese metal films to remove the conductive metal film and the barriermetal film other than the portions thereof lying inside of the trenches.

Next, after a second interlayer insulating film 17 is formed from asilicon oxide film or the like by the CVD method, using a photoresist asa mask, dry etching is performed and a contact hole to reach the gateelectrode 9 and a contact hole to reach source/drain regions areconcurrently formed. A barrier metal film is then formed on thesubstrate surface including the inside of the contact holes from Ti, TiNor a layered film of these, and thereafter a conductive metal film of Wor the like is formed by the CVD method or such so as to fill up thesecontact holes, and then CMP is applied to these metal films to removethe conductive metal film and the barrier metal film lying in regionsother than the inside of the contact holes. By this, as shown in FIG. 15and FIG. 16, a contact plug 18 to reach the gate electrode 9, andcontact plugs 19–26 to reach source/drain regions are concurrentlyformed. When etch back is performed, instead of the CMP, a localinterconnection (L₂) 27 as well as conductive film patterns 28–33 can beformed, in place of a method described below, by making the barriermetal film made of Ti, TiN or a layered film of these remain on thesurface and patterning this barrier metal film with a resist used as amask.

Next, a conductive film is formed from a TiN film or the like by thesputtering method or the CVD method, and patterning is applied to thisconductive film with a photoresist used as a mask, whereby a localinterconnection (L₂) 27 that is to be in contact with contact plugs 18,19 and 20 is formed, as shown in FIG. 17 and FIG. 18. Thereat, the localinterconnection (L₂) 27 is formed so that, seen from the top surface, aportion thereof overlaps, at least, a portion of the lower layer localinterconnection (L₁) 16 with the second interlayer insulating film 17lying therebetween. In the drawings, the local interconnection (L₂) 27is formed so as to overlap the entire top surface of the lower layerlocal interconnection (L₁) 16.

When patterning to form the local interconnection (L₂) 27 is carriedout, on contact plugs 21–26, rectangular conductive film patterns 28–33that are in contact therewith and covering the top surface thereof areconcurrently formed, respectively, in order to facilitate the connectionbetween respective contact plugs 21–26 and corresponding via plugs thatare to be formed later in upper layers.

Next, after a third interlayer insulating film 34 is formed from asilicon oxide film or the like by the CVD method, by applying dryetching thereto with a photoresist used as a mask, via holes to reachrespective conductive film patterns 28–33 are formed. A barrier metalfilm is then formed on the substrate surface including the inside of viaholes, and thereafter a conductive metal film is formed from W or thelike by the CVD method or such so as to fill up these via holes, and byapplying the CMP to these metal films, the conductive metal film and thebarrier metal film lying in regions other than the inside of the viaholes are removed, whereby via plugs 35–40 reaching respectiveconductive film patterns 28–33 are formed, as shown in FIG. 19 and FIG.20.

Next, on the third interlayer insulating film 34, a supply voltage line41 for applying a supply voltage V_(CC) and a reference voltage line 42for applying a reference voltage V_(SS) are formed, as shown in FIG. 2and FIG. 3. These interconnections can be formed by forming an aluminiumfilm on the third interlayer insulating film 34 by the sputtering methodor such, and thereafter applying dry etching thereto, with a photoresistused as a mask, to pattern the aluminium film. Thereat, instead of thealuminium film, there may be set a layered film for which layers of abarrier metal film (TiN film or the like), an aluminium film and ananti-reflection coating film (TiN film or the like) are laid insuccession. The supply voltage line 41 is in contact with via plugs 36and 37 and electrically connected to the source regions of the loadtransistors P₁ and P₂, respectively. The reference voltage line 42 is incontact with via plugs 35 and 38 and electrically connected to thesource regions of the driver transistors D₁ and D₂, respectively.

When patterning to form the supply voltage line 41 and the referencevoltage line 42 is carried out, on via plugs 39 and 40, rectangularconductive film patterns 43 and 44 that are in contact therewith andcovering the top surface thereof are concurrently formed respectively,in order to facilitate the connection between respective via plugs 39and 40 connected to one side of the source/drain regions of thetransmission transistors and the corresponding via plugs connected tobit lines BL₁ and BL₂ that are to be formed later, respectively.

Next, on the third interlayer insulating film 34 on which the supplyvoltage line 41, the reference voltage line 42 or the like are formed, afourth interlayer insulating film is formed from silicon oxide or thelike by the CVD method. Dry etching is then applied thereto with aphotoresist used as a mask, which forms via holes to reach conductivefilm patterns 43 and 44 which are formed on via plugs 39 and 40,respectively. Subsequently, after a barrier metal film is formed on thefourth interlayer insulating film including the inside of these viaholes, a conductive metal film is formed by the CVD method from W or thelike so as to fill up these via holes. The CMP is then performed toremove these metal films lying in regions other than the insides of viaholes, and thereby formation of via plugs are accomplished.

Next, on the fourth interlayer insulating film in which these via plugsare formed, bit lines BL₁ and BL₂ are formed. These bit lines can beformed by forming an aluminium film on the fourth interlayer insulatingfilm by the sputtering method or such, and thereafter applying dryetching thereto, with a photoresist used as a mask, to pattern thealuminium film. Thereat, instead of the aluminium film, there may be seta layered film for which layers of a barrier metal film (TiN film or thelike), an aluminium film and an anti-reflection coating film (TiN filmor the like) are laid in succession. The bit lines are in contact withone of via plugs formed in the fourth interlayer insulating film,respectively, and are electrically connected to one side of thesource/drain regions of one of the transmission transistors T₁ and T₂.

Through the steps described above, fabrication of a memory cell of thepresent embodiment is accomplished. After this, prescribed steps, forexample, of forming a passivation film on the fourth interlayerinsulating film on which bit lines are formed, may be performedappropriately.

The structure of the second embodiment that is described as anotherembodiment with reference to FIG. 21 can be formed as follows.

Following the step of forming a structure shown in FIG. 14 (the step offorming an inlaid interconnection 16 (L₁)), etch back is performed so asto make the top surface of the first interlayer insulating film 15 lowerthan the top surface of the inlaid interconnection 16 and exposepartially the lateral face of the inlaid interconnection.

Next, after a second interlayer insulating film 17 is formed from asilicon oxide film or the like by the CVD method, dry etching is appliedthereto, with a photoresist used as a mask, to form, concurrently, acontact hole to reach the gate electrode 9 and a contact hole to reachsource/drain regions. A barrier metal film is then formed from Ti, TiNor a layered film of these on the substrate surface including the insideof the contact holes, and thereafter a conductive metal film of W or thelike is formed by the CVD method or such so as to fill up these contactholes, and then etch back is applied to these metal films to remove theconductive metal film and the barrier metal film lying in regions otherthan the inside of the contact holes. By this, a contact plug 18 toreach the gate electrode 9, and contact plugs 19–26 to reachsource/drain regions are concurrently formed.

Next, a conductive film is formed from a TiN film or the like by thesputtering method or the CVD method, and patterning is applied to thisconductive film with a photoresist used as a mask, whereby a localinterconnection (L₂) 27 that is to be in contact with contact plugs 18,19 and 20 is formed, as shown in FIG. 21. Thereat, the localinterconnection (L₂) 27 is formed so that, seen from the top surface, aportion thereof overlaps, at least, a portion or the entire top surfaceof the lower layer local interconnection (L₁) (the inlaidinterconnection 16), with the second interlayer insulating film 17 lyingtherebetween, and besides it is disposed to cover the exposed lateralface of the inlaid interconnection 16, with the second interlayerinsulating film 17 lying therebetween.

As other embodiments of the present invention, structures capable toraise the capacitance of the capacitor element are described below.

Third Embodiment

A cross-sectional view showing a structure of the present embodiment ispresented in FIG. 23. FIGS. 23 (a) and (b) corresponds to FIGS. 3( a)and (b) showing a structure of the First Embodiment, respectively.

In the structure of the present embodiment, a stacked electrode 101 isdisposed on a lower layer local interconnection 16 (L₁) that is aninlaid interconnection. A plate-shaped upper layer local interconnection27 (L₂) is disposed so as to cover, at least, a portion of the topsurface as well as a portion of the lateral face of this stackedelectrode 101 with an insulating film 17 lying therebetween. Although,in the drawing, the top surface and the lateral face of the stackedelectrode 101 are partially covered, both of the faces can be entirelycovered, as far as the margin permits. In such a structure, a capacitorelement is formed also on the lateral face of the stacked electrode sothat the capacitance of the element can be significantly raised.

The structure of the present embodiment can be formed as follows.

After following the same steps as the First Embodiment, up to the oneillustrated in FIG. 14, DOPOS (Doped Polycrystalline Silicon), DOPOS-HSG(Hemi-Spherical Grain), TiN or the like is grown, as shown in FIG. 24,and, by patterning the formed conductive film by means of knownlithography, a stacked electrode 101 is formed on a lower layer localinterconnection 16 (L₁). In this patterning, a mask having the samepattern as for the lower layer local interconnection 16 (L₁) can beutilized. On the other hand, it is also possible to dispose the lowerlayer local interconnection 16 (L₁) and stacked electrode 101 in such away that, seen from the top with respect to the horizontal position,they may overlap partially with each other or one of them contain theother completely, as far as electrical conduction normally takes placeand the margin permits. After the stacked electrode is formed in thisway, a second interlayer insulating film 17 (a high-dielectric-constantfilm of SiO₂, SiN, TaO or such) that is to serve as a capacitorinsulating film is formed. After this, a contact plug 18 to reach thegate electrode 9, and contact plugs 19–26 to reach source/drain regionsare formed. Next, as shown in FIG. 25, a plate-shaped upper layer localinterconnection 27 (L₂) is formed, and then a third interlayerinsulating film 34 is formed to attain a structure shown in FIG. 26.Except that a stacked electrode 101 is set, and to cover this stackedelectrode the upper layer local interconnection 27 (L₂) is set and,resulting from the stacked electrode being set, the third interlayerinsulting film 34 is formed considerable thick, Third Embodiment can befabricated in the same way as First Embodiment.

Fourth Embodiment

A cross-sectional view showing a structure of the present embodiment ispresented in FIG. 27. FIGS. 27 (a) and (b) corresponds to FIGS. 3( a)and (b) showing a structure of the First Embodiment, respectively.

In the structure of the present embodiment, a trench is set in a thirdinterlayer insulating film 34 which is set, prior to an application of asecond interlayer insulating film 17 that is to serve as a capacitorinsulating film, and in this trench, there is formed a capacitor elementcomposed of a cylinder electrode (an electrode film in trench, takingthe shape of a hollow prism) 111 which covers the inside sidewall of thetrench and besides the bottom of which comes into contact with the lowerlayer local interconnection 16 (L₁) and a buried electrode 112 whichfills up the trench after a second interlayer insulating film 17 isapplied thereto, and the second interlayer insulating film 17 placedtherebetween. In such a structure, a capacitor element is formed also onthe sidewall of the trench so that the capacitance of the element canbe, significant raised.

The structure of the present invention can be fabricated as follows.

After following the same steps as the First Embodiment, up to the oneillustrated in FIG. 14, as shown in FIG. 28, a third interlayerinsulating film 34 is set and, on a lower layer local interconnection 16(L₁), a trench is formed so that, at least, part of the top surface ofthe lower layer local interconnection may be exposed. Next, after sconductive film of DOPOS, DOPOS-HSG, TiN or the like is grown and,coating of a resist is applied thereto and then etch back is applied tothe resist film to remove the resist lying outside of the trench. Next,etch back is applied to the conductive film to remove the conductivefilm lying outside of the trench and then the resist present inside ofthe trench is removed. As a result, a cylinder electrode (an electrodefilm in trench) 111 is formed on the inside surface of the trench (FIG.29). After that a second interlayer insulating film 17 (ahigh-dielectric-constant film of SiO₂, SiN, TaO or such) that is toserve as a capacitor insulating film is formed. In forming the trench, amask having the same pattern as for the lower layer localinterconnection 16 (L₁) can be utilized. On the other hand, it is alsopossible to dispose the lower layer local interconnection 16 (L₁) andcylinder electrode 111 in such a way that, seen from the top withrespect to the horizontal position, they may overlap partially with eachother or one of them contain the other completely, as far as electricalconduction normally takes place and the margin permits. Next, in a thirdinterlayer insulating film 34, there are formed via holes which reachcontact plugs set in the first interlayer insulating film 15. Next,within these via holes, a barrier metal film (Ti, TiN or a layered filmof TiN/Ti) is formed. Thereat, the inside of the trench may be filled upwith the barrier metal (to form a buried electrode 112). When the trenchis adequately large in width, the barrier metal film may be formed onthe inside of the trench and thereafter the trench may be filled up witha conductive material such as W. Subsequently, via hole are filled upwith a conductive material such as N and then etch back is appliedthereto, whereby the structure shown in FIG. 30 is attained. Hereat, thebarrier metal can be left on the substrate surface. Next, in the sameway as in a manufacturing method of First Embodiment, a plate-shapedupper layer local interconnection 27 (L₂) is formed, as shown in FIG.31, and thereafter, by forming a fifth interlayer insulating film 201, astructure shown in FIG. 32 is obtained. After that, in the same way asin a manufacturing method of First Embodiment, formation of a SRAMmemory cell is accomplished.

Fifth Embodiment

A cross-sectional view showing a structure of the present embodiment ispresented in FIG. 33. FIGS. 33 (a) and (b) corresponds to FIGS. 3( a)and (b) showing a structure of the First Embodiment, respectively.

In the structure of the present embodiment, a trench is set in a firstinterlayer insulating film 15, and in this trench, there is providedwith a lower layer local interconnection 16 (L₁) in the shape of hollowprism which covers the inside sidewall of the trench. The bottom face(the contacting face with the substrate) of the cylindrical lower layerlocal interconnection 16 (L₁) is of the same shape and in the samedisposition as the bottom face of the inlaid interconnection of FirstEmbodiment which is the lower layer interconnection (L₁) of thereof.Further, in that trench, there is formed a capacitor element composed ofthe cylindrical lower layer local interconnection 16 (L₁), a buriedelectrode 112 which fills up the trench after a second interlayerinsulating film 17 is applied thereto, and the second interlayerinsulating film 17 placed therebetween. In such a structure, a capacitorelement is formed also on the sidewall of the trench so that thecapacitance of the element can be significantly raised.

The structure of the present embodiment can be fabricated as follows.

A structure shown in FIG. 34 is formed in the same way as FirstEmbodiment, up to the step immediately before the step of filling up thetrench with a conductive material, as illustrated in FIG. 14. Next,after s conductive film of DOPOS, DOPOS-HSG, TiN or the like is grownand, coating of a resist is applied thereto and then etch back isapplied to the resist film to remove the resist lying outside of thetrench. Next, etch back is applied to the conductive film to remove theconductive film lying outside of the trench and then the resist presentinside of the trench is removed. As a result, a lower layer localinterconnection 16 (L₁) in the shape of a hollow prism is formed on theinside surface of the trench (FIG. 35). After that, a second interlayerinsulating film 17 (a high-dielectric-constant film of SiO₂, SiN, TaO orsuch) that is to serve as a capacitor insulating film is formed. Next,prescribed contact holes are formed in the first interlayer insulatingfilm 15 and, within these contact holes, a barrier metal film (Ti, TiNor a layered film of TiN/Ti) is formed. Thereat, the inside of thetrench may be filled up with the barrier metal (to form a buriedelectrode 112). When the trench is adequately large in width, thebarrier metal film may be formed on the inside of the trench andthereafter the trench may be filled up with a conductive material suchas W. Subsequently, contact holes are filled up with a conductivematerial such as W and then etch back is applied thereto, whereby thestructure shown in FIG. 36 is attained. Hereat, the barrier metal can beleft on the substrate surface. Next, in the same way as in amanufacturing method of First Embodiment, a plate-shaped upper layerlocal interconnection 27 (L₂) is formed, as shown in FIG. 37, andthereafter, by forming a third interlayer insulating film 34, astructure shown in FIG. 38 is obtained. After that, in the same way asin a manufacturing method of First Embodiment, formation of a SRAMmemory cell is accomplished.

1. A method of manufacturing a semiconductor memory device having a SRAMin which a memory cell comprises a pair of transmission transistors anda flip-flop circuit containing a pair of driver transistors and a pairof load transistors, which comprises the steps of: forming, on asemiconductor substrate, active regions to form respective sourceregions and drain regions of said driver transistors, said loadtransistors and said transmission transistors; forming, on saidsemiconductor substrate, a first conductive film; and thereafterpatterning this first conductive film to form a first conductive filminterconnection that is to serve as an interconnection to constituterespective gate electrodes of said driver transistors, said loadtransistors and said transmission transistors; forming, on saidsemiconductor substrate, a first insulating film; and thereafterforming, in this first insulating film, an inlaid interconnection as oneof a pair of local interconnections cross-coupling a pair ofinput/output terminals in said flip-flop circuit; and forming, on saidfirst insulating film, a second insulating film, and thereafter forminga second conductive film and, then, patterning this second conductivefilm to form a second conductive film interconnection as the other oneof said pair of local interconnections.
 2. A method of manufacturing asemiconductor memory device according to claim 1, wherein said secondconductive film interconnection is disposed so as to overlap at least aportion of a lop surface of said inlaid interconnection, with saidsecond insulating film lying therebetween; and said inlaidinterconnection and said second conductive film interconnection,together with said second insulating film lying therebetween, constitutea capacitor element.
 3. A method of manufacturing a semiconductor memorydevice according to claim 1, wherein: said inlaid interconnection isformed so as to come in contact with a drain region constituting a firstdriver transistor which is one of said pair of driver transistors; achain region constituting a first load transistor which is one of saidpair of load transistors and has a gate electrode formed from a firstconductive film interconnection A, the gate electrode being in common tosaid first driver transistor; and a first conductive filminterconnection B which constitutes a gate electrode of a second drivertransistor which is the other one of the pair of driver transistors aswell as a gate electrode of a second load transistor which is the otherone of the pair of load transistors; and said second conductive filminterconnection is formed to come into contact with every one of contactsections which are made by forming, concurrently, a contact hole toreach said first conductive film interconnection A, a contact hole toreach the drain region of said second driver transistor, and a contacthole to reach the drain region of said second load transistor; andthereafter filling up these contact holes with a conductive material. 4.A method of manufacturing a semiconductor memory device according toclaim 3, wherein said first conductive film interconnection B is formedinto the branched shape in which branching off takes place between thedrain region of said second driver transistor and the drain region ofsaid second load transistor, and said inlaid interconnection is formedso as to come into contact with this branched section ofinterconnection.
 5. A method of manufacturing a semiconductor memorydevice according to claim 1, which further comprises the step of forminga refractory metal silicide layer on the surface of every source regionsand drain regions of said pair of driver transistors, said pair of loadtransistors and said pair of transmission transistors as well as on thesurface of said first conductive film interconnection which constitutesgate electrodes thereof.
 6. A method of manufacturing a semiconductormemory device having a Static Random Access Memory (SRAM) cell,comprising the steps of: forming a first diffusion region and a seconddiffusion region on a semiconductor substrate; forming a firstconductive layer over the semiconductor substrate; forming an interlayerinsulating film on the semiconductor substrate; the interlayerinsulating film having an opening which exposes the first and seconddiffusion regions and the first conductive layer; forming a secondconductive layer in the opening and contacting the first and seconddiffusion regions; forming a dielectric layer on the second conductivelayer; and forming a third conductive layer on the dielectric layer,whereby a capacitor is formed by the second and third conductive layersand the dielectric layer.
 7. The method of manufacturing a semiconductormemory device according to claim 6, wherein a top surface of the secondconductive layer is higher than that of the interlayer insulating film.8. The method of manufacturing a semiconductor memory device accordingto claim 7, wherein the dielectric layer and the third conductive layerface the facing side surfaces of the second conductive layer.
 9. Themethod of manufacturing a semiconductor memory device according to claim8, wherein the dielectric layer and the third conductive layer face asingle side of the facing side surfaces of the second conductive layer.10. The method of manufacturing a semiconductor memory device accordingto claim 6, wherein the opening is filled with the second conductivelayer.
 11. The method of manufacturing a semiconductor memory deviceaccording to claim 6, wherein a top surface of the second conductivelayer is lower than that of the interlayer insulating film.
 12. Themethod of manufacturing a semiconductor memory device according to claim11, wherein the opening is filled with the third conductive layer. 13.The method of manufacturing a semiconductor memory device according toclaim 12, wherein the capacitor is formed on the inner side wall in theopening as well as on the bottom in the opening.
 14. The method ofmanufacturing a semiconductor memory device according to claim 6,wherein the SRAM cell comprises: a first load transistor having sourceand drain regions, one of which corresponds to the first diffusionregion, a first drive transistor having source and drain regions, one ofwhich corresponds to the second diffusion region, and a second loadtransistor and a second drive transistor, each of the second loadtransistor and the second drive transistor baying a gate electrode whichis formed of the first conductive layer.
 15. The method of manufacturinga semiconductor memory device according to claim 14, wherein the firstconductive layer has a “T” shape having two branches, one of thebranches corresponding to the gate electrode of the second loadtransistor and the other of the branches corresponding to the gateelectrode of the second drive transistor, and a trunk, a bottom of thetrunk directly contacting the second conductive layer.
 16. The method ofmanufacturing a semiconductor memory device according to claim 14,wherein: a first contact is connected between the third conductive layerand a gate electrode of the first load transistor and the first drivetransistor, a second contact is connected between the third conductivelayer and one of source and drain regions of the second load transistor,and a third contact is connected between the third conductive layer andone of source and drain regions of the second chive transistor.
 17. Themethod of manufacturing a semiconductor memory device according to claim14, further comprising the step of: forming a gate electrode of thefirst load transistor and the first drive transistor; forming a secondinterlayer insulating film as the dielectric layer on the secondconductive layer and the interlayer insulating film which has theopening; and forming a first contact hole which exposes the other ofsource and drain regions of the first load transistor, a second contacthole which exposes the other of source and drain regions of the firstdrive transistor, and a third contact hole which exposes the gateelectrode of the first load transistor and the first drive transistor,all the contact holes being formed in the same step, after forming thesecond interlayer insulating film.
 18. The method of manufacturing asemiconductor memory device according to claim 17, further comprisingthe step of forming a fourth and a fifth contact holes which expose eachof source and drain regions of the second load transistor and a sixthand a seventh contact holes which expose each of source and drainregions of the second drive transistor, wherein all the first to theseventh contact holes are formed in the same step.
 19. The method ofmanufacturing a semiconductor memory device according to claim 18,further comprising the step of burying a conductive material in all thecontact holes in the same step.
 20. The method of manufacturing asemiconductor memory device according to claim 17, further comprisingthe step of burying a conductive material in all the contact holes inthe same step.
 21. A method of manufacturing a semiconductor memorydevice having a SRAM in which a memory cell comprises a pair oftransmission transistors and a flip-flop circuit containing a pair ofdriver transistors and a pair of load transistors, which comprises thesteps of: forming, on a semiconductor substrate, active regions to formrespective source regions and drain regions of said driver transistors,said load transistors and said transmission transistors; forming, onsaid semiconductor substrate, a first conductive film; and thereafterpatterning this first conductive film to form a first conductive filminterconnection that is to serve as an interconnection to constituterespective gate electrodes of said driver transistors, said loadtransistors and said transmission transistors; forming, on saidsemiconductor substrate, a first insulating film, and thereafterforming, in this first insulating film, an inlaid interconnection as oneof a pair of local interconnections cross-coupling a pair ofinput/output terminals in said flip-flop circuit; exposing a part of alateral face of said inlaid interconnection; and forming a secondinsulating film on said first insulating film and the exposed section ofsaid inlaid interconnection; and thereafter forming a second conductivefilm and, then, patterning this second conductive film so as to overlapthe top surface and a portion of the lateral face of said inlaidinterconnection, with said second insulating film placed therebetween;and thereby forming a second conductive film interconnection whichconstitutes the other one of said pair of local interconnections, whichprovides a capacitor element composed of said second conductive filminterconnection and the top surface and a portion of the lateral face ofsaid inlaid interconnection, together with said second insulating filmlying therebetween.
 22. A method of manufacturing a semiconductor memorydevice according to claim 21, wherein: said inlaid interconnection isformed so as to come in contact with a drain region constituting a firstdriver transistor which is one of said pair of driver transistors; adrain region constituting a first load transistor which is one of saidpair of load transistors and has a gate electrode formed from a firstconductive film interconnection A, the gate electrode being in common tosaid first driver transistor; and a first conductive filminterconnection B which constitutes a gate electrode of a second drivertransistor which is the other one of the pair of driver transistors aswell as a gate electrode of a second load transistor which is the otherone of the pair of load transistors; and said second conductive filminterconnection is formed to come into contact wit every one of contactsections which are made by forming, concurrently, a contact hole toreach said first conductive film interconnection A, a contact hole toreach the drain region of said second driver transistor, and a contacthole to reach the drain region of said second load transistor; andthereafter filling up these contact holes with a conductive material.23. A method of manufacturing a semiconductor memory device according toclaim 21, which further comprises the step of forming a refractory metalsilicide layer on the surface of every source regions and drain regionsof said pair of driver transistors, said pair of load transistors andsaid pair of transmission transistors as well as on the surface of saidfirst conductive film interconnection which constitutes gate electrodesthereof.